Control system for a failure mode testing system

ABSTRACT

A control system for a failure mode testing system is described. The control system employs at least one control algorithm that enables the testing system to be operated at optimal pressure and frequency levels in order to generate a desired system response, such as a desired energy level and desired slope of the fast Fourier transform of the system response. Also described are a pressure dither system and a frequency ringing system for enhancing the operation of the actuator cylinders of the failure mode testing system. All three of the systems can be incorporated, either singularly or in combination, into a computer software program that can be employed to operate and control the failure mode testing system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/388,057 entitled “Control System for a FailureMode Testing System,” filed Mar. 23, 2006, now U.S. Pat. No. 7,136,769which is a continuation application of U.S. patent application Ser. No.10/770,859 entitled “Control System for a Failure Mode Testing System,”filed Feb. 3, 2004, now U.S. Pat. No. 7,024,323, which is a continuationapplication of U.S. patent application Ser. No. 10/260,037 entitled“Control System For a Failure Mode Testing System,” filed Apr. 17, 2001,now U.S. Pat. No. 6,697,746, which is a continuation application of U.S.patent application Ser. No. 09/427,456 entitled “Control System For aFailure Mode Testing System,” filed Oct. 26, 1999, now U.S. Pat. No.6,233,530, which is a continuation-in-part application of U.S. patentapplication Ser. No. 09/316,574 entitled “Design Maturity Algorithm,”filed May 21, 1999, now U.S. Pat. No. 6,247,366, which is acontinuation-in-part application of U.S. patent application Ser. No.08/929,839 entitled “Method and Apparatus For Optimizing the Design of aProduct,” filed Sep. 15, 1997, now U.S. Pat. No. 6,035,715, the entirespecifications of which are expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a new and improved control system for afailure mode testing system. The control systems employs at least onecontrol algorithm in order to optimize the performance of the failuremode testing system.

BACKGROUND OF THE INVENTION

The recent advent of failure mode testing systems to activate failuremodes has enabled manufacturers to discover latent defects or flawswhich may eventually lead to the failure of a product, component orsub-component. The methodology of these testing systems generallyinvolves the application of one or more types and/or levels of stimulito the product, component or sub-component until one or more failuremodes are activated. Typically, one of the stimuli includes vibration,such as that caused by striking a piston, rod, or other suitable device,against the product, component or sub-component itself, or a surface incontact with the product, component or sub-component. When the failuremode is activated, the failed product, component or sub-component isthen either repaired, replaced, or redesigned. This process may then berepeated in order to activate and eliminate other failure modes.

A proprietary testing system has been developed by Entela, Inc. (GrandRapids, Mich.) and is referred to as a failure mode verification testingsystem. This system, which is described in commonly-owned U.S. patentapplication Ser. No. 09/316,574 entitled “Design Maturity Algorithm”,filed May 21, 1999, now U.S. Pat. No. 6,247,366; and U.S. patentapplication Ser. No. 08/929,839 entitled “Method and Apparatus ForOptimizing the Design of Products”, filed Sep. 15, 1997, now U.S. Pat.No. 6,035,715, employs an apparatus which is capable of generating awide variety of stress patterns, especially six axis uniform randomstress patterns, in a product, component, or sub-component in order toactivate the failure modes of that particular product, component, orsub-component.

A six axis uniform random stress is generally defined as the stresshistory at a point having uniform random distribution with the stressbeing comprised of tension and compression stress in three orthogonalaxes and torsion stress about the same three orthogonal axes. Six axisuniform random stress patterns are generally defined as six axis uniformrandom stress at all points on a product such that the stress history ofthe six axis uniform random stress at each point forms a time history ofnon-repeating stress patterns.

The apparatus uses six axis uniform random actuation at one or moremounting locations of a product to produce six axis uniform randomstress patterns in the product. These six axis uniform random stresspatterns identify failure modes previously uncovered with other testingmethodologies. Furthermore, the simultaneous introduction of otherstimuli (at varying levels), such as temperature, vibration, pressure,ultraviolet radiation, chemical exposure, humidity, mechanical cycling,and mechanical loading, identify other failure modes associated with theproduct.

In order to create the six axis uniform random stress patterns in theproduct, the apparatus employs a plurality (preferably six) ofactuators, also referred to as force imparting members, that can beoperated either pneumatically, hydraulically, by a combination of bothpneumatic and hydraulic power, or any other force imparting mechanism. Aportion of the actuators, such as the cylinders, are typically mounted(including slidingly), either directly or indirectly, onto one or moresupport members.

If six actuators are being used, they are preferably arranged in pairs,each pair being set about 120 degrees apart from the other pair. Eachactuator is simply comprised of a cylinder acting in cooperation with apiston in order to produce force and torque upon a point of rotation.The pressure to each actuator is preferably cycled between maximumextend pressure and maximum retract pressure in a linear “saw-tooth”manner. The frequency for each actuator is slightly different. Thisdifference in frequency causes an interference pattern of the cycling asthe actuators come in and out of phase with each other. It is thisdifference in the frequencies of the actuators which creates a six axisuniform random stress in the product. By way of a non-limiting example,the six pneumatic actuators can be operated at frequencies of 1.8 Hz,1.9 Hz, 2.0 Hz, 2.1 Hz, 2.2 Hz, 2.3 Hz, and 2.4 Hz, respectively.Therefore, as the actuators come in and out of phase with one another,the frequency content in the center will go from about 2 Hz to infinity.It should be noted that other frequencies may be used for the individualactuators in order to produce an even lower frequency.

A portion of the actuators, such as the pistons, are typicallyconnected, either directly or indirectly, to a platform, such as a hub,upon which the product is mounted. As the actuators are actuated, theyproduce a force which generates a torque about a point of rotation onthe platform. It should be noted that whether a torque is generatedabout the point of rotation will depend upon which actuators are beingactuated and in what sequence with respect to one another. The force andtorque are eventually transferred from the platform to the productitself, thus creating the six axis uniform random stress patterns in theproduct.

During routine operation of the apparatus, it is not uncommon for theactuators to be cycled back and forth very rapidly. Therefore, it isimpractical to manually attempt to continuously adjust the variousoperational parameters that affect actuator operation, such as thepressure and frequency of the cylinders. The pressure parameter concernsthe amount of pressure in the air line (e.g., in a pneumatic system) incommunication with the cylinder of the actuator, which is typicallyexpressed in pounds per square inch (psi). The frequency parameterconcerns the frequency that each cylinder is set to, which is typicallyexpressed in Hertz (Hz).

By way of a non-limiting example, the system response of the apparatuscan be measured in terms of energy E (e.g., grms or peak G) and slope mof the fast Fourier transform (FFT) of the system response. A FFT istypically performed on a time history or a response. By way of anon-limiting example, an acceleration signal from an accelerometer wouldprovide a varying signal in time. The FFT of the acceleration signalwould give the acceleration level vs. frequency. From the FFT of theacceleration signal, the slope of the FFT plot (i.e., response level vs.frequency) can be determined.

Preferably, a desired energy level E having a desired slope m (e.g.,flat) is produced by the application of appropriate levels of pressureand frequency. For example, if the energy level were plotted on theY-axis of a graph and the frequency level were plotted on the X-axis ofthat same graph, the majority of data points could be bisected by a linehaving a slope substantially equal to zero. Thus, the energy level wouldbe substantially constant over the entire frequency range.

Due to the large number of calculations that would have to be performedon a split second basis for each of the six actuators, it is impracticalto manually perform the calculations, let alone make the requisiteadjustments to the operational parameters of the actuators, withoutadversely affecting the efficient performance of the testing system.Nonetheless, it is important to the optimal operation of the testingsystem that the desired performance parameters are achieved andmaintained during the course of the testing procedure.

Additionally, with respect to pressure, it has been observed that bykeeping each cylinder at a constant pressure, the actuators have atendency, due to frictional forces and historesis, to gravitate towardsa set point and get stuck, thus causing the actuators to improperlyfunction. For example, if the pressure is slightly too high, theapparatus will tend to drift up and then get stuck. Conversely, if thepressure is slightly too low, the apparatus will tend to drift down andthen get stuck.

Furthermore, with respect to frequency, it has been observed that bykeeping each cylinder at a specific individual frequency, over time oneof the actuators will receive less energy than the other actuators. Forexample, if one cylinder of an actuator pair is operated at 5 Hz at agiven pressure, and the other cylinder of the actuator pair is operatedat 5.5 at that same given pressure, then over time a little more energyis being given to one cylinder than the other. The fact that onecylinder receives more energy can be confirmed by calculating theintegration of the given pressure at the slightly higher frequency. As aresult, the apparatus will tend to drift toward the actuator having thelowest energy level, thus causing performance problems.

Therefore, there exists a need for a control system for determining ifthe desired system response of a failure mode testing system is or isnot present. The control system should be capable of quickly,accurately, and if needed, constantly adjusting the operationalparameters (e.g., pressure and frequency) until the desired systemresponse is achieved and subsequently maintained.

SUMMARY

General objects of the present invention are to facilitate and enhancetesting of products under various conditions, to provide morecomprehensive testing and to make testing more efficient by reducing theenergy, time, and expense required to undertake testing.

Another object of the present invention is to provide a new and improvedcontrol system for a failure mode testing system.

Still another object of the present invention is to provide a new andimproved control algorithm for a failure mode testing system.

In accordance with one embodiment of the present invention, a controlsystem for a failure mode testing system having a determinable systemresponse is provided, wherein the testing system includes a plurality ofactuator cylinders, each cylinder operating at an initial pressure andan initial frequency, wherein the frequency of each of the cylinders isdifferent, comprising:

-   -   a) selecting a desired system response;    -   b) determining the system response;    -   c) determining whether the desired system response is present;        and    -   d) changing an operational parameter of the cylinders by a        sufficient amount in order to achieve the desired system        response, wherein the operational parameter is selected from the        group consisting of pressure, frequency, and combinations        thereof.

A more complete appreciation of the present invention and its scope canbe obtained from understanding the accompanying drawings, which arebriefly summarized below, the followed detailed description of theinvention, and the appended claims.

DRAWINGS

FIG. 1 is a schematic of a control system for a failure mode testingsystem, in accordance with one aspect of the present invention;

FIG. 2 is a schematic of a pressure dither system for a failure modetesting system, in accordance with one aspect of the present invention;

FIG. 3 is a schematic of a frequency ringing system for a failure modetesting system, in accordance with one aspect of the present invention;

FIG. 4 is a schematic of a computer software program for a controlsystem for a failure mode testing system, in accordance with one aspectof the present invention; and

FIG. 5 is a schematic of an alternative computer software program for acontrol system for a failure mode testing system, in accordance with oneaspect of the present invention.

The same reference numerals refer to the same parts throughout thevarious Figures.

DETAILED DESCRIPTION

In accordance with one embodiment of the present invention, a controlsystem employing at least one control algorithm is provided for use inconjunction with a failure mode testing system. The control algorithmenables the testing system to be operated at optimal pressure andfrequency levels in order to generate a desired system response. Thecontrol algorithm can be incorporated into a computer software programthat can be employed to control and operate the failure mode testingsystem (e.g., a control system).

The control algorithm of the present invention is actually comprised ofa number of discrete algorithms, each of which generally determine asingle piece of information, based on data provided by various inputsources, such as sensors, detectors, data storage mediums, and so forth.

By way of a non-limiting example, one set of algorithms determines thechange in energy due to pressure, the change in energy due to frequency,the change in slope due to pressure, and the change in slope due tofrequency. That information is then utilized by additional algorithms todetermine the average energy and slope of the system response. Thatinformation is then utilized by still additional algorithms to determinethe new target energy and slope of the system response. Finally, thatinformation is utilized by still yet another set of algorithms todetermine the new target frequency and pressure to achieve the newtarget energy and slope of the system response.

With reference to FIG. 1, there is illustrated a schematic view of anon-limiting example of a control system employing at least one controlalgorithm, in accordance with one embodiment of the present invention.The control algorithm is intended to be used in conjunction with afailure mode testing system employing an apparatus that is capable ofproducing six axis uniform random stress patterns in a product.

As shown in condition box 10, and by way of a non-limiting example, theactuators of the apparatus are assigned a pre-selected default pressure(P) and a pre-selected default frequency (F). These pre-selecteddefaults are set by the operator, and, of course, it should be notedthat they may be changed or altered to meet the desired operationalparameters of the testing system. Additionally, the pressure change (dp)is set at 10 psi (although any other figure may be substitutedtherefor), the frequency change (df) is set at 0.5 Hz (although anyother figure may be substituted therefor), and the step frequency (f) isset at 0.2 Hz (although any other figure may be substituted therefor).

As shown in box 20, and by way of a non-limiting example, the pressureof the actuator cylinder is set to P+dp. Each of the actuator cylindersare set to different frequencies, F1, F2, F3, F4, F5, and F6,respectively. F1 is equal to F+f+df. The step frequency (f) is used to“step” the base frequency up to six distinct frequencies, i.e. adifferent frequency for each cylinder, as will become apparent from thefollowing description. F2 is equal to F+2f+df, F3 is equal to F+3f+df,F4 is equal to F+4f+df, F5 is equal to F+5f+df, and F6 is equal toF+6f+df. Thus, all six of the actuator cylinders have a differentfrequency.

At this point, the testing system is permitted to operate, in that theactuators are actuated. As shown in box 30, and by way of a non-limitingexample, the system response (e.g., of the cylinders) is measured,calculated, or otherwise determined, specifically the energy level (E),expressed in rms, peak G, or any other appropriate unit, and the slopem, expressed as the slope of the fast Fourier transform of the systemresponse (i.e., time history which is the slope of the energy vs. thefrequency plot).

This information is then stored in a data storage medium and/or device(e.g., RAM, hard drive, floppy disk, CD-ROM, or the like) as anappropriate variable, under four different conditions, i.e., highpressure/high frequency (HH), high pressure/low frequency (HL), lowpressure/high frequency (LH), and low pressure/low frequency (LL).

As shown in box 40, and by way of a non-limiting example, the systemresponse information generated is stored as eight different variables,i.e., E_(LL) (measured E when both P and F are low), E_(LH) (measured Ewhen P is low and F is high), E_(HL) (measured E when P is high and F islow), E_(HH) (measured E when both P and F are high), m_(LL) (measured mwhen both P and F are low, m_(LH) (measured m when P is low and F ishigh), m_(HL) (measured M when P is high and F is low), and m_(HH)(measured m when both P and F are high).

At this point, decision node 50 is encountered which queries whether allfour conditions have been tried (i.e., high/high, high/low, low/high,and low/low).

If all four conditions have not been tried, the control system prompts achange in either the pressure, frequency, and/or both, of the individualactuators, so that all four conditions are tried. As shown in Box 60,and by way of a non-limiting example, assuming that the first conditionwas low frequency/low pressure, then the first time change requires ahigh frequency/low pressure condition, the second time change requires ahigh frequency/high pressure condition, and the third time changerequires a low frequency/high pressure condition. It should be notedthat the sequence of these conditions may in any desired order. Thecritical consideration is that all four conditions have been tried, notthe order in which they are tried. The method of changing the pressureand/or frequency is by adding or removing appropriate levels of pressure(i.e., ±dp) and/or frequency (i.e., ±df).

To illustrate this concept, consider the following non-limiting example.Assume that the default P is 30 psi, and the dp is 10 psi. Therefore,the initial pressure is set at 40 psi (i.e., P (30 psi)+dp (10 psi)=40psi), which represents the “high” pressure condition (i.e., “plus” dp).Now, assume that the default frequency is 2 Hz, the step frequency is0.2 Hz, and the df is 0.5 Hz. Therefore, the frequency of the firstcylinder (F1) is 2.7 Hz (i.e., F (2 Hz)+f (0.2 Hz)+df (0.5 Hz)=2.7 Hz),the second cylinder (F2) is 2.9 Hz (i.e., F (2 Hz)+2f (0.4 Hz)+df (0.5Hz)=2.9 Hz), the third cylinder (F3) is 3.1 Hz (i.e., F (2 Hz)+3f (0.6Hz)+df (0.5 Hz)=3.1 Hz), the fourth cylinder (F4) is 3.3 Hz (i.e., F (2Hz)+4f (0.8 Hz)+df (0.5 Hz)=3.3 Hz), the fifth cylinder (F5) is 3.5 Hz(i.e., F (2 Hz)+5f (1.0 Hz)+df (0.5 Hz)=3.5 Hz), and the sixth cylinder(F6) is 3.7 Hz (i.e., F (2 Hz)+6f (1.2 Hz)+df (0.5 Hz)=3.7 Hz), all ofwhich represent the “high” frequency condition (i.e., “plus” df).

The apparatus is now operated under this particular high pressure/highfrequency condition, the system response is measured (Box 30), and theenergy/slope variables are calculated and stored (Box 40), and thendecision node 50 is encountered. As only one condition has been tried(i.e., high pressure/high frequency), the control system will prompt theapparatus to try the three remaining conditions (i.e., high pressure/lowfrequency, low pressure/low frequency, and low pressure/high frequency).

With respect to the high pressure/low frequency condition, instead ofadding the df Hz amount to each of the individual frequencies of theactuators, it is removed or subtracted. Therefore, the frequency of thefirst cylinder (F1) is 1.7 Hz (i.e., F (2 Hz)+f (0.2 Hz)+df (−0.5Hz)=1.7 Hz), the second cylinder (F2) is 1.9 Hz (i.e., F (2 Hz)+2f (0.4Hz)+df (−0.5 Hz)=1.9 Hz), the third cylinder (F3) is 3.1 Hz (i.e., F (2Hz)+3f (0.6 Hz)+df (−0.5 Hz)=2.1 Hz), the fourth cylinder (F4) is 2.3 Hz(i.e., F (2 Hz)+4f (0.8 Hz)+df (−0.5 Hz)=2.3 Hz), the fifth cylinder(F5) is 2.5 Hz (i.e., F (2 Hz)+5f (1.0 Hz)+df (−0.5 Hz)=2.5 Hz), and thesixth cylinder (F6) is 2.7 Hz (i.e., F (2 Hz)+6f (1.2 Hz)+df (−0.5Hz)=2.7 Hz), all of which represent the “low” frequency condition (i.e.,“minus” df).

The apparatus is now operated under this particular high pressure/lowfrequency condition, the system response is measured (Box 30), and theenergy/slope variables are calculated and stored (Box 40), and thendecision node 50 is again encountered. As only two conditions have beentried (i.e., high pressure/high frequency, high pressure/low frequency),the control system will prompt the apparatus to try the two remainingconditions (i.e., low pressure/low frequency and low pressure/highfrequency).

With respect to the low pressure/low frequency condition, thefrequencies remain in the “low” condition; however, instead of addingthe dp psi amount to the pressure of the actuators, it is removed orsubtracted. Therefore, the pressure of all the cylinders is 20 psi(i.e., P (30 psi)−dp (10 psi)=20 psi), which represents the “low”pressure condition (i.e., “minus” dp).

The apparatus is now operated under this particular low pressure/lowfrequency condition, the system response is measured (Box 30), and theenergy/slope variables are calculated and stored (Box 40), and thendecision node 50 is again encountered. As only three conditions havebeen tried (i.e., high pressure/high frequency, high pressure/lowfrequency, low pressure/low frequency), the control system will promptthe apparatus to try the last remaining condition (i.e., and lowpressure/high frequency).

With respect to the low pressure/high frequency condition, the pressureremains in the “low” condition; however, instead of subtracting the dfHz amount to the frequencies of each of the actuators, it is added.Therefore, the frequency of the first cylinder (F1) is 2.7 Hz (i.e., F(2 Hz)+f (0.2 Hz)+df (0.5 Hz)=2.7 Hz), the second cylinder (F2) is 2.9Hz (i.e., F (2 Hz)+2f (0.4 Hz)+df (0.5 Hz)=2.9 Hz), the third cylinder(F3) is 3.1 Hz (i.e., F (2 Hz)+3f (0.6 Hz)+df (0.5 Hz)=3.1 Hz), thefourth cylinder (F4) is 3.3 Hz (i.e., F (2 Hz)+4f (0.8 Hz)+df (0.5Hz)=3.3 Hz), the fifth cylinder (F5) is 3.5 Hz (i.e., F (2 Hz)+5f (1.0Hz)+df (0.5 Hz)=3.5 Hz), and the sixth cylinder (F6) is 3.7 Hz (i.e., F(2 Hz)+6f (1.2 Hz)+df (0.5 Hz)=3.7 Hz), all of which represent the“high” frequency condition (i.e., “plus” df).

The apparatus is now operated under this particular low pressure/highfrequency condition, the system response is measured (Box 30), and theenergy/slope variables are calculated and stored (Box 40), and thendecision node 50 is again encountered. As all four conditions have nowbeen tried (i.e., high pressure/high frequency, high pressure/lowfrequency, low pressure/low frequency, and low pressure/high frequency),the system will then perform the calculations of the algorithms shown inBox 70.

The first algorithm, shown below:Dep=((E _(HH) +E _(HL))−(E _(LH) +E _(LL)))/(2dp)is used to determine the change in energy due to pressure (Dep).

The second algorithm, shown below:Def=((E _(HH) +E _(LH))−(E _(HL) +E _(LL)))/(2df)is used to determine the change in energy due to frequency (Def).

The third algorithm, shown below:Dsp=((m _(HH) +m _(HL))−(m _(LH) +m _(LL)))/(2dp)is used to determine the change in slope due to pressure (Dsp).

The fourth algorithm, shown below:Dsf=((m _(HH) +m _(LH))−(m _(HL) +m _(LL)))/(2df)is used to determine the change in slope due to frequency (Dsf).

The fifth algorithm, shown below:E 1=average (E _(HH) ,E _(HL) ,E _(LH) ,E _(LL))is used to determine the average energy for the high pressure/highfrequency, high pressure/low frequency, low pressure/high frequency, andlow pressure/low frequency conditions.

The sixth algorithm, shown below:S 1=average (m _(HH) ,m _(HL) ,m _(LH) ,m _(LL))is used to determine the average slope for the high pressure/highfrequency, high pressure/low frequency, low pressure/high frequency, andlow pressure/low frequency conditions.

The seventh algorithm, shown below:E 2 =E 1+(E _(DESIRED) −E 1)/nwherein n is greater than 1, is used to determine the new target energy(E2). It should be noted that the desired energy (E_(DESIRED)) ispre-selected by the operator.

The eighth algorithm, shown below:S 2 =S 1+(S _(DESIRED) −S 1)/nwherein n is greater than 1, is used to determine the new target slope(S2). It should be noted that the desired slope (S_(DESIRED)) ispre-selected by the operator.

The ninth algorithm, shown below:F _(NEW)=[(DspE 2 −DspE 1 −DepS 2+DepS 1 −DepDsfF)/(DefDsp−DepDsf)]is used to determine the new target frequency (F_(NEW)) to achieve thenew target energy (E2). Once the F_(NEW) is determined, it replaces F asthe default frequency.

The tenth algorithm, shown below:P _(NEW)=[(DsfE 2 −DsfE 1 −DefS 2 +DefS 1+DepDsfP−DefDspP)/(DefDsp−DepDsf)]is used to determine the new target pressure (P_(NEW)) to achieve thenew target slope (S2). Once the P_(NEW) is determined, it replaces P asthe default pressure.

Once all of the calculations have been performed for the above-describedalgorithms, the system is then prompted to determine whether theE_(DESIRED) and the S_(DESIRED) conditions have been satisfied, as shownin Box 80. The determination with respect to the E_(DESIRED) and theS_(DESIRED) conditions are calculated according to the followingformulas:E _(LL) <E _(DESIRED) <E _(HH)andm _(LL) <S _(DESIRED) <m _(HH)wherein if both the E_(DESIRED) and the S_(DESIRED) conditions fallbetween their respective formulaic extremes, the system is prompted tonarrow the search, as shown in Box 90. The search is narrowed bydividing the dp and the df by n, respectively, wherein n is a numbergreater than 1. This has the intended effect of decreasing the amount ofchange in pressure and frequency, thus reducing the E_(LL)/E_(HH) andm_(LL)/m_(HH) ranges, respectively. The entire cycle is then repeated(starting at Box 20) with the new pressure and frequency defaults (i.e.,P_(NEW) and F_(NEW)), and is continued until the E_(DESIRED) and theS_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH)ranges, respectively. By way of a non-limiting example, the cycle couldbe repeated until the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH) rangesare within a pre-selected percentage of the E_(DESIRED) and theS_(DESIRED,) respectively. This process is continuously repeated duringthe operation of the apparatus to ensure that both the E_(DESIRED) andthe S_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH)ranges.

However, if either one of the E_(DESIRED) and the S_(DESIRED) conditionsdo not fall between their respective formulaic extremes, the system isprompted to expand the search, as shown in Box 100. The search isexpanded by either multiplying the dp and the df by n (wherein n is anumber greater than 1), respectively, depending on whether theE_(DESIRED) or the S_(DESIRED) fell outside of the respective range.This has the intended effect of increasing the amount of change inpressure and/or frequency thus increasing the E_(LL)/E_(HH) and/orm_(LL)/m_(HH) ranges, respectively. The entire cycle is then repeated(starting at Box 20) with the new pressure and frequency defaults (i.e.,P_(NEW) and F_(NEW)), and is continued until the E_(DESIRED) and/or theS_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and/or m_(LL)/m_(HH)ranges, respectively. By way of a non-limiting example, the cycle couldbe repeated until the expanded E_(LL)/E_(HH) and m_(LL)/m_(HH) rangesare within a pre-selected percentage of the E_(DESIRED) and theS_(DESIRED,) respectively. This process is continuously repeated duringthe operation of the apparatus to ensure that both the E_(DESIRED) andthe S_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH)ranges.

In accordance with another embodiment of the present invention, apressure dither system is provided for use in conjunction with a failuremode testing system. The pressure dither system will overcome thepreviously described problem of actuators having a tendency, due tofrictional forces and historesis, to gravitate towards a set point andget stuck, thus causing the actuators to improperly function.

Pressure dither involves the application and/or subtraction of a smallamount of pressure to or from the cylinder, generally on the order ofabout 1-2 psi, either above or below the default pressure P and thechange in pressure dp.

The reason for employing a pressure dither is enhanced controllability.If the cylinder of the actuator is constantly at a fixed pressure, evenwhen running at the “high” pressure condition, it will gravitate to aset point and get stuck, as previously described. By dithering thepressure a slight amount, i.e., fluctuating the pressure slightly, thisunwanted situation can be avoided. Specifically, the extension and/orretraction pressure of the actuator cylinder is preferably slightlydifferent (i.e., higher and/or lower as compared to the fixed pressure)during each cycle, therefore, the probability that the cylinder will getstuck is decreased. It should be noted that the pressure dither systemcan be used either independent of, or in conjunction with the controlsystem of the present invention.

With reference to FIG. 2, there is illustrated a schematic view ofpressure dither system for a failure mode testing system, in accordancewith one embodiment of the present invention. The pressure dither systemcan be incorporated into a software program that can be employed tocontrol and operate the failure mode testing system.

By way of a non-limiting example, an algorithm for determining pressuredither (ditherp) is shown below:ditherp=[((rnd)(maxdither))−((rnd)(maxdither2))]wherein rnd is a random number function between 0 and 1, and maxditheris the pre-selected maximum pressure difference for pressure dither(ditherp).

By way of a non-limiting example, the ditherp could be expressed asfollows, assuming a rnd=1 and a maxdither of 1 psi were employed:ditherp=[(1)(1 psi)]−[(1)(1 psi)(2)]=−0.5 psi

Thus, the ditherp would be −0.5 psi in this case, meaning that thepressure to the cylinder would be dithered by −0.5 psi. Once the ditherphas been determined, the pressure during the extend phase (Extend) andretract phase (Retract) can then be calculated according to thefollowing algorithms:Extend=P+ditherpwherein P is the default pressure, and ditherp is the pressure dither,andRetract=P+difference+ditherpwherein P is the default pressure, difference is a pre-selected pressuredifference between the extend and retract pressures, and ditherp is thepressure dither.

By way of a non-limiting example, the Extend pressure could be expressedas follows, assuming a P=30 psi and a ditherp of −0.5 psi were employed:Extend=30 psi+(−0.5 psi)=29.5 psi

By way of a non-limiting example, the Retract pressure could beexpressed as follows, assuming a P=30 psi, a difference (i.e., pressuredifference between the extend and retract pressures) of 5 psi, and aditherp of −0.5 psi were employed:Retract=30 psi+5 psi+(−0.5 psi)=34.5 psi

Although the afore-mentioned pressure dither system algorithms areespecially suited for creating and maintaining the pressure dithersystem of the present invention, it should be noted that any othersuitable system or method for altering or changing the default pressuresupplied to the cylinder can be employed as well.

In accordance with yet another embodiment of the present invention, afrequency ringing system is provided for use in conjunction with afailure mode testing system. The frequency ringing system will overcomethe previously described problem of actuators receiving less energy thanthe other actuators, causing the apparatus to drift toward the actuatorhaving the lowest energy level, resulting in performance problems.

The frequency ringing system involves reordering the frequency assignedto a particular cylinder. The reordering can either be random or cycled.The frequency ringing system does not involve changing the amount of anyparticular frequency itself (that is controlled by the control system,specifically the control algorithm), but only the location of where thatfrequency is vis-a-vis the cylinders.

To illustrate this concept, consider the following non-limiting example.Assume that the six actuator cylinders are assigned the followingrespective frequencies: Cylinder 1—2 Hz; Cylinder 2—2.5 Hz, Cylinder 3—3Hz; Cylinder 4—3.5 Hz, Cylinder 5—4 Hz; and Cylinder 6—4.5 Hz. Now, ifthese frequencies did not change during the course of the testingprocedure, the apparatus would have a tendency to drift towards Cylinder1, as it has the lowest frequency, and as explained previously, thelowest energy. Therefore, the present invention overcomes this problemby indexing, reordering or reassigning the various frequencies,regardless of their magnitude, to each of the cylinders so that no onecylinder remains at the same frequency for any extended period of time.It should be noted that present invention does not employ a simplerotation of the frequencies, i.e., moving the frequencies in orderaround the adjacent actuators, as that permits the formation of a“moving” or “roving” low energy actuator location. Therefore, instead ofthe low energy actuator being found at one particular actuator location,the low energy actuator is moving around all six actuator locations insequence. The reordering of the frequencies, in accordance with presentinvention, avoids this problem.

The time interval between the random assignments can be for any lengthand can be either fixed or random. To illustrate this concept, assumethat the cylinders originally are set at the following frequencies:Cylinder 1—2 Hz; Cylinder 2—2.5 Hz, Cylinder 3—3 Hz; Cylinder 4—3.5 Hz,Cylinder 5—4 Hz; and Cylinder 6—4.5 Hz, and that the frequency ringingsystem has been programmed to randomly reorder the frequencies every onesecond, for a total of six seconds. As a non-limiting example, thefrequency information for each cylinder could look like that presentedin Table 1 below:

TABLE 1 Cyl.# Init. Time 1 Time 2 Time 3 Time 4 Time 5 Time 6 Freq.Freq. Freq. Freq. Freq. Freq. Freq. (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) 12 2.5 4.5 3 4 3.5 2 2 2.5 4.5 2 4 3 2.5 3.5 3 3 2 3.5 2.5 4.5 3 4 4 3.53 2.5 3.5 2 4 4.5 5 4 3.5 4 2 2.5 4.5 3 6 4.5 4 3 4.5 3.5 2 2.5

As can be seen from Table 1, the cylinder location of the frequencieslisted above differ after each second has elapsed, therefore, no onecylinder retains the same frequency for any extended period of time. Itshould be noted that the frequency ringing system can be used eitherindependent of, or in conjunction with either the control system and/orthe pressure dither system of the present invention.

With reference to FIG. 3, there is illustrated a schematic view offrequency ringing system for a failure mode testing system, inaccordance with one embodiment of the present invention. The frequencyringing system can be incorporated into a software program that can beemployed to control and operate the failure mode testing system.

By way of a non-limiting example, an algorithm for determining frequencyringing is shown below:Cylinder i=Mode(i+Mode(C 1, 6),)+1wherein i is the cylinder number (i.e., a number between 1 and 6), Modeis the remainder of the quotient between any two given numbers, and C1is the count number (e.g., any number representing a status change inthe cylinder frequency location). Thus, count 1 is denoted herein as C1,count 2 is denoted as C2, and so forth. Each cylinder is assigned aninitial frequency (e.g., cylinder 1 is assigned frequency 1 (F1),cylinder 2 is assigned frequency 2 (F2), and so forth); thus, as thefrequency is indexed or reordered at each count, the frequency assignedto a particular cylinder is changed (which can be abbreviated as cyli).

By way of a non-limiting example, the frequency ringing system asapplied to cylinders 1-6 through an eight count series (e.g., 1-8) isillustrated below:

-   Count 1    -   Cylinder 1=Mode(1+Mode(1, 6),6)+1    -   Cylinder 1=Mode(1+1,6)+1    -   Cylinder 1=Mode(2,6)+1    -   Cylinder 1=2+1    -   Cylinder 1=3    -   Thus, cylinder 1 at count 1 is assigned frequency 3.-   Count 2    -   Cylinder 1=Mode(1+Mode(2, 6),6)+1    -   Cylinder 1=Mode(1+2,6)+1    -   Cylinder 1=Mode(3,6)+1    -   Cylinder 1=3+1    -   Cylinder 1=4    -   Thus, cylinder 1 at count 2 is assigned frequency 4.-   Count 3    -   Cylinder 1=Mode(1+Mode(3, 6),6)+1    -   Cylinder 1=Mode(1+3,6)+1    -   Cylinder 1=Mode(4,6)+1    -   Cylinder 1=4+1    -   Cylinder 1=5    -   Thus, cylinder 1 at count 3 is assigned frequency 5.-   Count 4    -   Cylinder 1=Mode(1+Mode(4, 6),6)+1    -   Cylinder 1=Mode(1+4,6)+1    -   Cylinder 1=Mode(5,6)+1    -   Cylinder 1=5+1    -   Cylinder 1=6    -   Thus, cylinder 1 at count 4 is assigned frequency 6.-   Count 5    -   Cylinder 1=Mode(1+Mode(5, 6),6)+1    -   Cylinder 1=Mode(1+5,6)+1    -   Cylinder 1=Mode(6,6)+1    -   Cylinder 1=0+1    -   Cylinder 1=1    -   Thus, cylinder 1 at count 5 is assigned frequency 1.-   Count 6    -   Cylinder 1=Mode(1+Mode(6, 6),6)+1    -   Cylinder 1=Mode(1+0,6)+1    -   Cylinder 1=Mode(1,6)+1    -   Cylinder 1=1+1    -   Cylinder 1=2    -   Thus, cylinder 1 at count 6 is assigned frequency 2.-   Count 7    -   Cylinder 1=Mode(1+Mode(7, 6),6)+1    -   Cylinder 1=Mode(1+7,6)+1    -   Cylinder 1=Mode(8,6)+1    -   Cylinder 1=2+1    -   Cylinder 1=3    -   Thus, cylinder 1 at count 7 is assigned frequency 3.-   Count 8    -   Cylinder 1=Mode(1+Mode(8, 6),6)+1    -   Cylinder 1=Mode(1+8,6)+1    -   Cylinder 1=Mode(9,6)+1    -   Cylinder 1=3+1    -   Cylinder 1=4    -   Thus, cylinder 1 at count 8 is assigned frequency 4.

By way of a non-limiting example, the frequency ringing system asapplied to cylinder 2 through an eight count series (e.g., 1-8) isillustrated below:

-   Count 1    -   Cylinder 2=Mode(2+Mode(1, 6),6)+1    -   Cylinder 2=Mode(2+1,6)+1    -   Cylinder 2=Mode(3,6)+1    -   Cylinder 2=3+1    -   Cylinder 2=4    -   Thus, cylinder 2 at count 1 is assigned frequency 4.-   Count 2    -   Cylinder 2=Mode(2+Mode(2, 6),6)+1    -   Cylinder 2=Mode(2+2,6)+1    -   Cylinder 2=Mode(4,6)+1    -   Cylinder 2=4+1    -   Cylinder 2=5    -   Thus, cylinder 2 at count 2 is assigned frequency 5.-   Count 3    -   Cylinder 2=Mode(2+Mode(3, 6),6)+1    -   Cylinder 2=Mode(2+3,6)+1    -   Cylinder 2=Mode(5,6)+1    -   Cylinder 2=5+1    -   Cylinder 2=6    -   Thus, cylinder 2 at count 3 is assigned frequency 6.-   Count 4    -   Cylinder 2=Mode(2+Mode(4, 6),6)+1    -   Cylinder 2=Mode(2+4,6)+1    -   Cylinder 2=Mode(6,6)+1    -   Cylinder 2=0+1    -   Cylinder 2=1    -   Thus, cylinder 2 at count 4 is assigned frequency 1.-   Count 5    -   Cylinder 2=Mode(2+Mode(5, 6),6)+1    -   Cylinder 2=Mode(2+5,6)+1    -   Cylinder 2=Mode(7,6)+1    -   Cylinder 2=1+1    -   Cylinder 2=2    -   Thus, cylinder 2 at count 5 is assigned frequency 2.-   Count 6    -   Cylinder 2=Mode(2+Mode(6, 6),6)+1    -   Cylinder 2=Mode(2+0,6)+1    -   Cylinder 2=Mode(2,6)+1    -   Cylinder 2=2+1    -   Cylinder 2=3    -   Thus, cylinder 2 at count 6 is assigned frequency 3.-   Count 7    -   Cylinder 2=Mode(2+Mode(7, 6),6)+1    -   Cylinder 2=Mode(2+7,6)+1    -   Cylinder 2=Mode(9,6)+1    -   Cylinder 2=3+1    -   Cylinder 2=4    -   Thus, cylinder 2 at count 7 is assigned frequency 4.-   Count 8    -   Cylinder 2=Mode(2+Mode(8, 6),6)+1    -   Cylinder 2=Mode(2+8,6)+1    -   Cylinder 2=Mode(10,6)+1    -   Cylinder 2=4+1    -   Cylinder 2=5

Thus, cylinder 2 at count 8 is assigned frequency 5.

By way of a non-limiting example, the frequency ringing system asapplied to cylinder 3 through an eight count series (e.g., 1-8) isillustrated below:

-   Count 1    -   Cylinder 3=Mode(3+Mode(1, 6),6)+1    -   Cylinder 3=Mode(3+1,6)+1    -   Cylinder 3=Mode(4,6)+1    -   Cylinder 3=4+1    -   Cylinder 3=5    -   Thus, cylinder 3 at count 1 is assigned frequency 5.-   Count 2    -   Cylinder 3=Mode(3+Mode(2, 6),6)+1    -   Cylinder 3=Mode(3+2,6)+1    -   Cylinder 3=Mode(5,6)+1    -   Cylinder 3=5+1    -   Cylinder 3=6    -   Thus, cylinder 3 at count 2 is assigned frequency 6.-   Count 3    -   Cylinder 3=Mode(3+Mode(3, 6),6)+1    -   Cylinder 3=Mode(3+3,6)+1    -   Cylinder 3=Mode(6,6)+1    -   Cylinder 3=0+1    -   Cylinder 3=1    -   Thus, cylinder 3 at count 3 is assigned frequency 1.-   Count 4    -   Cylinder 3=Mode(3+Mode(4, 6),6)+1    -   Cylinder 3=Mode(3+4,6)+1    -   Cylinder 3=Mode(7,6)+1    -   Cylinder 3=1+1    -   Cylinder 3=2    -   Thus, cylinder 3 at count 4 is assigned frequency 2.-   Count 5    -   Cylinder 3=Mode(3+Mode(5, 6),6)+1    -   Cylinder 3=Mode(3+5,6)+1    -   Cylinder 3=Mode(8,6)+1    -   Cylinder 3=2+1    -   Cylinder 3=3    -   Thus, cylinder 2 at count 5 is assigned frequency 3.-   Count 6    -   Cylinder 3=Mode(3+Mode(6, 6),6)+1    -   Cylinder 3=Mode(3+0,6)+1    -   Cylinder 3=Mode(3,6)+1    -   Cylinder 3=3+1    -   Cylinder 3=4    -   Thus, cylinder 2 at count 6 is assigned frequency 4.-   Count 7    -   Cylinder 3=Mode(3+Mode(7, 6),6)+1    -   Cylinder 3=Mode(3+7,6)+1    -   Cylinder 3=Mode(10,6)+1    -   Cylinder 3=4+1    -   Cylinder 3=5    -   Thus, cylinder 3 at count 7 is assigned frequency 5.-   Count 8    -   Cylinder 3=Mode(3+Mode(8, 6),6)+1    -   Cylinder 3=Mode(3+8,6)+1    -   Cylinder 3=Mode(11,6)+1    -   Cylinder 3=5+1    -   Cylinder 3=6    -   Thus, cylinder 3 at count 8 is assigned frequency 6.

By way of a non-limiting example, the frequency ringing system asapplied to cylinder 4 through an eight count series (e.g., 1-8) isillustrated below:

-   Count 1    -   Cylinder 4=Mode(4+Mode(1, 6),6)+1    -   Cylinder 4=Mode(4+1,6)+1    -   Cylinder 4=Mode(5,6)+1    -   Cylinder 4=5+1    -   Cylinder 4=6    -   Thus, cylinder 4 at count 1 is assigned frequency 6.-   Count 2    -   Cylinder 4=Mode(4+Mode(2, 6),6)+1    -   Cylinder 4=Mode(4+2,6)+1    -   Cylinder 4=Mode(6,6)+1    -   Cylinder 4=0+1    -   Cylinder 4=1    -   Thus, cylinder 4 at count 2 is assigned frequency 1.-   Count 3    -   Cylinder 4=Mode(4+Mode(3, 6),6)+1    -   Cylinder 4=Mode(4+3,6)+1    -   Cylinder 4=Mode(7,6)+1    -   Cylinder 4=1+1    -   Cylinder 4=2    -   Thus, cylinder 4 at count 3 is assigned frequency 2.-   Count 4    -   Cylinder 4=Mode(4+Mode(4, 6),6)+1    -   Cylinder 4=Mode(4+4,6)+1    -   Cylinder 4=Mode(8,6)+1    -   Cylinder 4=2+1    -   Cylinder 4=3    -   Thus, cylinder 4 at count 4 his assigned frequency 3.-   Count 5    -   Cylinder 4=Mode(4+Mode(5, 6),6)+1    -   Cylinder 4=Mode(4+5,6)+1    -   Cylinder 4=Mode(9,6)+1    -   Cylinder 4=3+1    -   Cylinder 4=4    -   Thus, cylinder 4 at count 5 is assigned frequency 4.-   Count 6    -   Cylinder 4=Mode(4+Mode(6, 6),6)+1    -   Cylinder 4=Mode(4+0,6)+1    -   Cylinder 4=Mode(4,6)+1    -   Cylinder 4=4+1    -   Cylinder 4=5    -   Thus, cylinder 4 at count 6 is assigned frequency 5.-   Count 7    -   Cylinder 4=Mode(4+Mode(7, 6),6)+1    -   Cylinder 4=Mode(4+1,6)+1    -   Cylinder 4=Mode(5,6)+1    -   Cylinder 4=5+1    -   Cylinder 4=6    -   Thus, cylinder 4 at count 7 is assigned frequency 6.-   Count 8    -   Cylinder 4=Mode(4+Mode(8, 6),6)+1    -   Cylinder 4=Mode(4+2,6)+1    -   Cylinder 4=Mode(6,6)+1    -   Cylinder 4=0+1    -   Cylinder 4=1    -   Thus, cylinder 4 at count 8 is assigned frequency 1.

By way of a non-limiting example, the frequency ringing system asapplied to cylinder 5 through a six count series (e.g., 1-6) isillustrated below:

-   Count 1    -   Cylinder 5=Mode(5+Mode(1, 6),6)+1    -   Cylinder 5=Mode(5+1,6)+1    -   Cylinder 5=Mode(6,6)+1    -   Cylinder 5=0+1    -   Cylinder 5=1    -   Thus, cylinder 5 at count 1 is assigned frequency 1.-   Count 2    -   Cylinder 5=Mode(5+Mode(2, 6),6)+1    -   Cylinder 5=Mode(5+2,6)+1    -   Cylinder 5=Mode(7,6)+1    -   Cylinder 5=1+1    -   Cylinder 5=2    -   Thus, cylinder 5 at count 2 is assigned frequency 2.-   Count 3    -   Cylinder 5=Mode(5+Mode(3, 6),6)+1    -   Cylinder 5=Mode(5+3,6)+1    -   Cylinder 5=Mode(8,6)+1    -   Cylinder 5=2+1    -   Cylinder 5=3    -   Thus, cylinder 5 at count 3 is assigned frequency 3.-   Count 4    -   Cylinder 5=Mode(5+Mode(4, 6),6)+1    -   Cylinder 5=Mode(5+4,6)+1    -   Cylinder 5=Mode(9,6)+1    -   Cylinder 5=3+1    -   Cylinder 5=4    -   Thus, cylinder 5 at count 4 is assigned frequency 4.-   Count 5    -   Cylinder 5=Mode(5+Mode(5, 6),6)+1    -   Cylinder 5=Mode(5+5,6)+1    -   Cylinder 5=Mode(10,6)+1    -   Cylinder 5=4+1    -   Cylinder 5=5    -   Thus, cylinder 5 at count 5 is assigned frequency 5.-   Count 6    -   Cylinder 5=Mode(5+Mode(6, 6),6)+1    -   Cylinder 5=Mode(5+0,6)+1    -   Cylinder 5=Mode(5,6)+1    -   Cylinder 5=5+1    -   Cylinder 5=6    -   Thus, cylinder 5 at count 6 is assigned frequency 6.-   Count 7    -   Cylinder 5=Mode(5+Mode(7, 6),6)+1    -   Cylinder 5=Mode(5+1,6)+1    -   Cylinder 5=Mode(6,6)+1    -   Cylinder 5=0+1    -   Cylinder 5=1    -   Thus, cylinder 5 at count 7 is assigned frequency 1.-   Count 8    -   Cylinder 5=Mode(5+Mode(8, 6),6)+1    -   Cylinder 5=Mode(5+2,6)+1    -   Cylinder 5=Mode(7,6)+1    -   Cylinder 5=1+1    -   Cylinder 5=2    -   Thus, cylinder 5 at count 8 is assigned frequency 2.

By way of a non-limiting example, the frequency ringing system asapplied to cylinder 6 through an eight count series (e.g., 1-8) isillustrated below:

-   Count 1    -   Cylinder 6=Mode(6+Mode(1, 6),6)+1    -   Cylinder 6=Mode(6+1,6)+1    -   Cylinder 6=Mode(7,6)+1    -   Cylinder 6=1+1    -   Cylinder 6=2    -   Thus, cylinder 6 at count 1 is assigned frequency 2.-   Count 2    -   Cylinder 6=Mode(6+Mode(2, 6),6)+1    -   Cylinder 6=Mode(6+2,6)+1    -   Cylinder 6=Mode(8,6)+1    -   Cylinder 6=2+1    -   Cylinder 6=3    -   Thus, cylinder 6 at count 2 is assigned frequency 3.-   Count 3    -   Cylinder 6=Mode(6+Mode(3, 6),6)+1    -   Cylinder 6=Mode(6+3,6)+1    -   Cylinder 6=Mode(9,6)+1    -   Cylinder 6=3+1    -   Cylinder 6=4    -   Thus, cylinder 6 at count 3 is assigned frequency 4.-   Count 4    -   Cylinder 6=Mode(6+Mode(4, 6),6)+1    -   Cylinder 6=Mode(6+4,6)+1    -   Cylinder 6=Mode(10,6)+1    -   Cylinder 6=4+1    -   Cylinder 6=5    -   Thus, cylinder 6 at count 4 is assigned frequency 5.-   Count 5    -   Cylinder 6=Mode(6+Mode(5, 6),6)+1    -   Cylinder 6=Mode(6+5,6)+1    -   Cylinder 6=Mode(11,6)+1    -   Cylinder 6=5+1    -   Cylinder 6=6    -   Thus, cylinder 6 at count 5 is assigned frequency 6.-   Count 6    -   Cylinder 6=Mode(6+Mode(6, 6),6)+1    -   Cylinder 6=Mode(6+0,6)+1    -   Cylinder 6=Mode(6,6)+1    -   Cylinder 6=0+1    -   Cylinder 6=1    -   Thus, cylinder 6 at count 6 is assigned frequency 1.-   Count 7    -   Cylinder 6=Mode(6+Mode(7, 6),6)+1    -   Cylinder 6=Mode(6+1,6)+1    -   Cylinder 6=Mode(7,6)+1    -   Cylinder 6=1+1    -   Cylinder 6=2    -   Thus, cylinder 6 at count 7 is assigned frequency 2.-   Count 8    -   Cylinder 6=Mode(6+Mode(8, 6),6)+1    -   Cylinder 6=Mode(6+2,6)+1    -   Cylinder 6=Mode(8,6)+1    -   Cylinder 6=2+1    -   Cylinder 6=3    -   Thus, cylinder 6 at count 8 is assigned frequency 3.

The corresponding cylinder frequencies of the various cylinders at eachof the eight counts is presented in Table 2, below:

TABLE 2 Cyl.# C1 C2 C3 C4 C5 C6 C7 C8 Cyl.# Cyl.# Cyl.# Cyl.# Cyl.#Cyl.# Cyl.# Cyl.# Freq. Freq. Freq. Freq. Freq. Freq. Freq. Freq. 1 2 34 5 6 1 2 3 2 3 4 5 6 1 2 3 4 3 4 5 6 1 2 3 4 5 4 5 6 1 2 3 4 5 6 5 6 12 3 4 5 6 1 6 1 2 3 4 5 6 1 2

As can be seen from Table 2, the frequency initially assigned to aparticular cylinder location is being indexed or reordered among the sixcylinders in such a manner that after each count, an individualcylinder's frequency has changed. Additionally, it should be noted thatthe frequencies are not indexed in a sequential manner such that thefrequencies initially assigned to adjacent cylinders move lock steparound in a circle. As previously noted, that would merely cause thelow-energy site to move circularly around the actuator assemblies. Thepresent invention avoids this problem by ensuring that, sometime duringa count sequence, at least one individual cylinder has a frequency of anon-adjacent cylinder.

Thus, after each count, the frequency of a particular cylinder ischanged according to the following algorithm:C 1 =C 1+1wherein C1 is the count number (e.g., any number representing a statuschange in the cylinder frequency location). Thus after count 1, thefrequency of a particular cylinder would be changed to thatcorresponding to count 2, and so forth.

Although the afore-mentioned frequency ringing system algorithms areespecially suited for creating and maintaining the frequency ringingsystem of the present invention, it should be noted that any othersuitable system or method for indexing the frequencies assigned to thecylinders can be employed as well.

As previously mentioned, the control system, the pressure dither system,and the frequency ringing system, can be incorporated into computersoftware programs, either independently or combined in variouscombinations.

With reference to FIG. 4, there is illustrated a schematic view of acomputer software program for a control system for a failure modetesting system, in accordance with one embodiment of the invention.

With reference to FIG. 5, there is illustrated a schematic view of acomputer software program for a control system for a failure modetesting system employing both a pressure dither system and a frequencyringing system, in accordance with one embodiment of the invention.

The foregoing description is considered illustrative only of theprinciples of the invention. Furthermore, since numerous modificationsand changes will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and processshown as described above. Accordingly, all suitable modifications andequivalents may be resorted to falling within the scope of the inventionas defined by the claims which follow.

1. A control system for a failure mode testing system having adeterminable system response, wherein the testing system comprises: aplurality of actuator cylinders, each cylinder operating at a pressureand a frequency, wherein the frequency of each of the cylinders isdifferent, the system configured to perform the steps of: a) selecting adesired energy level of the system response; b) selecting a desiredslope of a function describing the system response; c) determining anenergy level under a high pressure/high frequency condition and a lowpressure/low frequency condition so as to define an energy level range;d) determining the slope of the function of the system response under ahigh pressure/high frequency condition and the low pressure/lowfrequency condition so as to define a slope range; e) adjusting theoutput of the actuator cylinders so the desired energy level fallswithin an energy level range; and f) adjusting the output of theactuator cylinders so the desired slope of the function describing thesystem response falls within the slope range.
 2. The control system inaccordance with claim 1, further comprising: g) decreasing the pressureand repeating steps a) through f), if the desired energy level of thesystem response is above the energy level range.
 3. The control systemin accordance with claim 1, further comprising: h) increasing thepressure and repeating steps a) through f), if the desired energy levelof the system response is below the energy level range.
 4. The controlsystem in accordance with claim 1, further comprising: i) decreasing thefrequency and repeating steps a) through f), if the desired slope of thefunction describing the system response does fall within the sloperange.
 5. The control system in accordance with claim 1, furthercomprising: j) increasing the frequency and repeating steps a) throughf), if the desired slope of the function describing the system responsedoes not fall within the slope range.
 6. The control system inaccordance with claim 1, further comprising: a pressure dither system,wherein the pressure of the actuator cylinder during extension andretraction is changed by an incremental amount of pressure (ditherp). 7.The control system in accordance with claim 6, wherein the ditherpressure (ditherp) is calculated in accordance with the formula:[((rnd)(maxdither))−((rnd)(maxdither2))], wherein rnd is a random numberfunction between 0 and 1, and maxdither is the pre-selected maximumpressure difference for dither pressure (ditherp).
 8. The control systemin accordance with claim 1, further comprising: a frequency ringingsystem, wherein the location of a particular frequency is reorderedamong the plurality of actuator cylinders.
 9. The control system inaccordance with claim 8, wherein the frequency ringing system iscalculated in accordance with the formula: cylinder i=Mode(i+Mode(C1,6),6)+1, wherein i is the cylinder number, Mode is the remainder of thequotient between any two given numbers, and C1 is the count numberrepresenting a status change in the cylinder frequency location.
 10. Acontrol system for a failure mode testing system having a determinablesystem response, wherein the testing system includes a plurality ofactuator cylinders, each cylinder operating at an initial pressure andan initial frequency, wherein the frequency of each of the cylinders isdifferent, comprising a processor configured to perform the steps of: a)selecting a desired system response; b) providing a signal to change aplurality of operational parameters of the cylinders by a pre-selectedamount in order to create a first pressure/frequency condition, whereinthe operational parameters are selected from the group consisting ofpressure, frequency, and combinations thereof; c) determining the systemresponse under the first pressure/frequency condition; and d) storingthe system response determination of the first pressure/frequencycondition in a data storage medium.
 11. The control system in accordancewith claim 10, further comprising: e) changing an operational parameterof the cylinders by a pre-selected amount in order to create a secondpressure/frequency condition different from the first pressure/frequencycondition; and f) determining the system response under the secondpressure/frequency condition.
 12. The control system in accordance withclaim 11, further comprising: g) storing the system responsedetermination of the second pressure/frequency condition in a datastorage medium.
 13. The control system in accordance with claim 12,further comprising: h) changing an operational parameter of thecylinders by a pre-selected amount in order to create a thirdpressure/frequency condition different from the first and secondpressure/frequency conditions; and i) determining the system responseunder the third pressure/frequency condition.
 14. The control system inaccordance with claim 13, further comprising: j) storing the systemresponse determination of the third pressure/frequency condition in adata storage medium.
 15. The control system in accordance with claim 14,further comprising: k) changing an operational parameter of thecylinders by a pre-selected amount in order to create a fourthpressure/frequency condition different from the first, second, and thirdpressure/frequency conditions; and l) determining the system responseunder the fourth pressure/frequency condition.
 16. The control system inaccordance with claim 15, further comprising: m) storing the systemresponse determination of the fourth pressure/frequency condition in adata storage medium.
 17. The control system in accordance with claim 16,further comprising: n) determining whether the desired system responseis present.
 18. The control system in accordance with claim 17, furthercomprising: o) decreasing the pre-selected amount that the operationalparameter is changed by and repeating steps b) through n), until thedesired system response is present.
 19. The control system in accordancewith claim 18, further comprising: p) increasing the pre-selected amountthat the operational parameter is increased by and repeating steps b)through n), until the desired system response is present.